A gas turbine engine comprises a compressor with one or several stages supplying a combustion chamber producing hot gases which drive one or more turbine rotors. The latter are connected to and drive the compressor rotors.
In particular, a compressor consists of several stages, each comprising a disc of rotating blades and stator vanes forming guide vanes. The rotating blades accelerate the airflow tangentially and compress it, whilst the guide vanes guide the airflow produced by the rotor blades so that the airflow leaving the stator vanes lies within the engine axis. In the high pressure section, the upstream stages of the guide vanes are generally variably angled. They are pivot-mounted so that they may be set at an angle with respect to the engine axis. A guide vane stage, within the scope of the present invention, consists more precisely of a plurality of independent stator vanes attached at one end to the compressor casing and extended at the other end by a lower pivot. The pivots are connected together by an inner ring which delimits the inner wall of the gas flow.
The inner ring may be circumferential in a single piece or preferably consisting of a plurality of sectors, at least two in semi-circles. The inner stator ring carries sealing members cooperating with mating sealing members on the rotor which oppose gas back-flow towards upstream. A prior art assembly can be seen in FIGS. 1 and 2. A stator vane pivot 2 is retained by a dowel 3 in a housing of the ring or ring sector 4. The stator vane is not shown in full. It extends radially outwardly through the gas stream and is fixed to the outer casing.
Ring 2 is held integral with vanes 2 by means of a determined number of keys 5 arranged around the inner stator ring. The keys are arranged either side of the pivot 21 of a vane as can be seen FIG. 2, across the dowel 3. Dowel 3 is crimped onto the vane so as to block any movement separating one from the other. Pivots 21 with their pad are freely rotatable and limited axially by the clearance between the keys and the keyway grooves in the pads with respect to the inner ring. The keys, distributed along the ring, together ensure the centering of the inner ring with respect to the stator vanes. The vanes themselves are retained at their other end, not shown, by the engine structure.
In this prior art example, the inner ring 2 carries a support for a sealing member 6. This sealing member, such as a honeycombed wear-resistant material, cooperates with a mating member on the rotor. Here it comprises a cylindrical part 61 which, towards upstream with respect to the direction of the gas flow, has an angle bracket 62 whose axial portion is housed in a circumferential groove with axial opening made in the upstream surface of ring 2. The cylindrical part bears against the radial inner side of ring 2. The cylindrical element 62 is locked in axial direction by a radial rib 62′. This bears upon the wall of ring 2 which faces downstream. A webbing 63 of substantially frustum shape dips downstream towards the rotor shaft. It comprises an annular housing 65 for the sealing member which is not illustrated. A vertical cowling 66 joins housing 65 upstream to a groove with axial opening facing downstream and provided in ring 2.
To prevent their self rotation leading to corrosion problems through ring friction, the keys comprise an axial shimming head 51. These heads comprise a flat part 53 in which the upper edge of element 62′ is housed. Immobilisation in axial direction, as shown, is therefore achieved with the radial rib 62′. One assembly mode comprises the following successive phases. The stator vanes are placed in position. They are held in position by their upper end. The inner ring or inner ring sectors are placed in position by engaging the pivots in housings 42. Ring 2 is immobilised using the keys which also ensure its centering. In an inner ring sector prepared for this purpose, the ring sectors carrying the sealing member support are inserted and caused to slide one after the other inside groove 22 until they are brought to their final position. With this arrangement the assembly is locked in position.
This structure has the disadvantage that it may deform under the action of axial aerodynamic forces exerted by the upstream gases. Instability phenomena therefore occur which are difficult to control.
In addition, as part of the constant desire to improve engine performance in aeronautics, it is sought to reduce the weight of component parts as much as possible.